Voltage-dependent potassium (Kv) channels conduct potassium ions (K+) across cell membranes in response to changes in the membrane voltage and thereby can regulate cellular excitability by modulating (increasing or decreasing) the electrical activity of the cell.
Functional Kv channels exist as multimeric structures formed by the association of four alpha and four beta subunits. The alpha subunits comprise six transmembrane domains, a pore-forming loop and a voltage-sensor and are arranged symmetrically around a central pore. The beta or auxiliary subunits interact with the alpha subunits and can modify the properties of the channel complex to include, but not be limited to, alterations in the channel's electrophysiological or biophysical properties, expression levels or expression patterns.
Functional Kv channels can exist as multimeric structures formed by the association of either identical or dissimilar Kv alpha and/or Kv beta subunits.
Nine Kv channel alpha subunit families have been identified and are termed Kv1-Kv9. As such, there is an enormous diversity in Kv channel function that arises as a consequence of the multiplicity of sub-families, the formation of both homomeric and heteromeric subunits within sub-families and the additional effects of association with beta subunits (M. J. Christie, Clinical and Experimental Pharmacology and Physiology, 1995, 22 (12), 944-951).
The Kv7 channel family consists of at least five members which include one or more of the following mammalian channels: Kv7.1, Kv7.2, Kv7.3, Kv 7.4, Kv7.5 and any mammalian or non-mammalian equivalent or variant (including splice variants) thereof. Alternatively, the members of this family are termed KCNQ1, KCNQ2, KCNQ3, KCNQ4 and KCNQ5 respectively (Dalby-Brown. W et al., Current Topics in Medicinal Chemistry, 2006, 6, 999-1023).
The five members of this family differ in their expression patterns. The expression of Kv 7.1 is restricted to the heart, peripheral epithelial and smooth muscle, whereas the expression of Kv 7.2-Kv 7.4 is limited to the nervous system to include the hippocampus, cortical neurons and dorsal root ganglion neurons (for a review see Delmas. P & Brown. D, Nature, 2005, 6, 850-862).
The neuronal Kv7 channels have been demonstrated to play key roles in controlling neuronal excitation. Kv7 channels, in particular Kv 7.2/Kv 7.3 heterodimers, underlie the M-current, aslowly activating, non-inactivating potassium current found in a number of neuronal cell types. The current has a characteristic time- and voltage-dependence that results in stabilisation of the membrane potential in response to multiple excitatory stimuli. In this way, the M-current is central to controlling neuronal excitability (for a review see Delmas. P & Brown.D, Nature, 2005, 6, 850-862).
The Kv7 channels are also clinically valuable targets, since mutations in the genes of four out of the five members gives rise to a number of human disorders. For example, mutations in the genes for KCNQ2 or KCNQ3 result in a form of juvenile epilepsy called benign familial neonatal convulsions (BNFC) (Jentsch, T. J., Nature Reviews Neuroscience, 2000, 1 (1), 21-30).
Thus, given the key physiological role of Kv7 channels in the nervous system and the involvement of these channels in a number of diseases, the development of modulators of Kv7 channels is very desirable.
Modulators of KCNQ2, KCNQ3 or KCNQ2/3 have potential utility in the treatment, prevention, inhibition, amelioration or alleviation of symptoms of a number of conditions or disease states including:
“Lower Urinary Tract Disorders”, this encompasses both painful (any lower urinary tract disorder involving sensations or symptoms that a patient subjectively describes as producing or resulting in pain) and non-painful lower urinary tract disorders (any lower urinary tract disorder involving sensations or symptoms, including mild or general discomfort, that is subjectively described as not producing or resulting in pain). “Lower urinary tract disorders” also includes any lower urinary tract disorder characterised by overactive bladder with and/or without loss of urine, urinary frequency, urinary urgency, and nocturia. Thus, lower urinary tract disorders includes overactive bladder or overactive urinary bladder (including, overactive detrusor, detrusor instability, detrusor hyperreflexia, sensory urgency and the symptoms of detrusor overactivity), urge incontinence or urinary urge incontinence, stress incontinence or urinary stress incontinence, lower urinary tract symptoms including obstructive urinary symptoms such as slow urination, dribbling at the end of urination, inability to urinate and/or the need to strain to urinate at an acceptable rate or irritating symptoms such as frequency and/or urgency. Lower urinary tract disorders may also include neurogenic bladder that occurs as the result of neurological damage due to disorders including but not limited to stroke, Parkinson's disease, diabetes, multiple sclerosis, peripheral neuropathy, or spinal cord lesions. Lower urinary tract disorders may also include prostatitis, interstitial cystitis, benign prostatic hyperplasia, and, in spinal cord injured patients, spastic bladder.
“Anxiety and Anxiety-Related Conditions”, this includes, but is not limited to, anxiety, generalized anxiety disorder, panic anxiety, obsessive compulsive disorder, social phobia, performance anxiety, post-traumatic stress disorder, acute stress reaction, adjustment disorders, hypochondriacal disorders, separation anxiety disorder, agoraphobia and specific phobias. Specific anxiety related phobias include, but are not limited to, fear of animals, insects, storms, driving, flying, heights or crossing bridges, closed or narrow spaces, water; blood or injury, as well as extreme fear of inoculations or other invasive medical or dental procedures.
“Epilepsy”, includes, but is not limited to, one or more of the following seizures: simple partial seizures, complex partial seizures, secondary generalised seizures, generalised seizures including absence seizures, myoclonic seizures, clonic seizures, tonic seizures, tonic clonic seizures and atonic seizures.
“Pain Disorders”, includes but is not limited to one or more on the following: acute pain such as musculoskeletal pain, post-operative pain and surgical pain; chronic pain such as chronic inflammatory pain (e.g. rheumatoid arthritis and osteoarthritis), neuropathic pain (e.g. post-herpetic neuralgia, trigeminal neuralgia and sympathetically-maintained pain) and pain associated with cancer and fibromyalgia; pain associated with migraine; pain (both chronic and acute), and/or fever and/or inflammation of conditions such as rheumatic fever; symptoms associated with influenza or other viral infections, such as the common cold; lower back and neck pain; headache; toothache; sprains and strains; myositis; neuralgia; synovitis; arthritis, including rheumatoid arthritis; degenerative joint diseases, including osteoarthritis; gout and ankylosing spondylitis; tendinitis; bursitis; skin-related conditions, such as psoriasis, eczema, burns and dermatitis; injuries, such as sports injuries and those arising from surgical and dental procedures.
“Gynaecological Pain”, for example, dysmenorrhoea, labour pain and pain associated with endometriosis.
“Cardiac Arrhythmias”, include, but are not limited to, atrial fibrillation, atrial flutter, atrial arrhythmia and supaventricular tachycardia.
“Thromboembolic Events” such as stroke.
“Cardiovascular Diseases” such as angina pectoris, hypertension and congestive heart failure.
“Disorders of the Auditory System” such as tinnitus.
“Migraine”
“Inflammatory and Immunological Diseases” (or a disorder involving immunosuppression) including inflammatory bowel disease, rheumatoid arthritis, graft rejection, asthma, chronic obstructive pulmonary disease, multiple sclerosis, cystic fibrosis and atherosclerosis.
“Gastrointestinal Disorders” including reflux oesophagitis, functional dyspepsia, motility disorders (including constipation and diarrhoea), and irritable bowel syndrome.
“Vascular and Visceral Smooth Muscle Disorders” including asthma, pulmonary hypertension, chronic obstructive pulmonary disease, adult respiratory distress syndrome, peripheral vascular disease (including intermittent claudication), venous insufficiency, impotence, cerebral and coronary spasm and Raynaud's disease.
“Cell Proliferative Disorders” including restenosis and cancer (including leukemia); treating or preventing gliomas including those of lower and higher malignancy.
“Metabolic Disorders” such as diabetes (including diabetic retinopathy, diabetic nephropathy and diabetic neuropathy), insulin resistance/insensitivity and obesity.
“Memory Loss” including Alzheimer's disease and dementia.
Other “CNS-Mediated Motor Dysfunction Disorders” including Parkinson's disease and ataxia.
“Ophthalmic Disorders” such as ocular hypertension.
Retigabine is an anti-epileptic drug whose mechanism of action involves potassium channel opening activity in neuronal cells (first described in European Patent No. 0554543). Retigabine enhances potassium currents through specific activation of KCNQ2/3 channels (Wickenden, A. D., Molecular Pharmacology, 2000, 58, 591-600). However, retigabine has been reported to have multiple effects in neuronal cells. These include sodium and calcium channel blocking activity (Rundfeldt, C, 1995, Naunyn-Schmiederberg's Arch Pharmacol, 351 (Suppl): R160) and effects on GABA (γ-aminobutyric acid) synthesis and transmission in rat neurons (Kapetanovic, I. M., 1995, Epilepsy Research, 22, 167-173, Rundfeldt, C, 1995, Naunyn-Schmiederberg's Arch Pharmacol, 351 (Suppl):R160).
Thus, in order to overcome unwanted side effects, more selective Kv7 channel modulators are required.
WO04035037 discloses the use of N-phenylanthranilic acid derivatives as modulators of KCNQ2, KCNQ3 and KCNQ2/3 channels. These derivatives have substituents comprising hydroxyalkyl or polyalkylene glycol moieties that are linked to one of the phenyl groups of the N-phenylanthranilic acid moiety via a variety of linkers. There is no disclosure of any compounds having a sulphonamide linker group.
It would be desirable to identify more selective Kv7 channel modulators for the prophylaxis or treatment of a number of disease states including lower urinary tract disorders, inflammatory and immunological diseases and pain indications. Using potassium ion channel patch clamp assays on KCNQ2, KCNQ3 and KCNQ2/3 channels recombinatly expressed in cells lines, a new family of N-phenylanthranilic acid compounds has been found that are excellent selective modulators of potassium ion flux through KCNQ2, KCNQ3 and/or KCNQ2/3 channels.